Nope, a modpack is a "fake DLC" which pretends to be behaving like Brave New World. You do not run it as a mod, you only need to have it (active) as a DLC and you start the game without going through the mods screen. It makes mods playable in multiplayer and the game also loads quicker.
There is a special way for creating it described on the VP wiki and even somewhere here. But if you are not familiar with it, I would not bother with learning it.
Because either way, to identify the problem, the best way is making sure that you have the base conditions same as others and no other mods is influencing it. So really, start a new game without the other mods and post a save (hey, even better, post more saves from different timings!) when the unhappiness problems occur.